Antilock brake system and antilock skid control systems (ABS/ABSR) and restraint systems (RHS) are state of the art as independent systems. ABS and ASR are often combined into a single system, referred to herein as ABSR. RHS refers to systems including, e.g. air bags and belt tighteners.
They make use of electronic control apparatus on the basis of microcontrollers for processing the controls and steering algorithms. The circuitry of these apparatus is similar: on the one hand due to processing of the sensor signals through the signal chain, digital signal processing, and power output to operate actuators, and on the other hand due to the need for error-proof protective structures, condition for systems with responsibility for safety (redundancy, test cycles etc.). The typical structure of electronic controls responsible for safety is represented in FIG. 1.
Therein, 1 is an input circuit for the sensor signals, 2a and 2b are two microprocessors for the redundant processing of the sensor signals, 3 a power output block for the operation of actuators, 4 a so-called surveillance and safety circuit, and 5 a relay with a switch with which a shut-down of the system is effected if an error is detected.
As regards the sensing system there is another thing common to both. Both systems make use of sensors which on the one hand, by measuring the wheel speed, and on the other hand by measuring the vehicle acceleration or deceleration, give indications of the dynamic behavior of the vehicle.